Depression is a very common disorder and can affect people at any age. Antidepressant drugs have been shown to be very effective in alleviating depression and improving mood. There are three general classes of antidepressant drugs: the tricyclics, heterocyclics and MAO inhibitors. These all work via different neurochemical mechanisms. The tricyclics (TCAs) have been shown to be most effective for a large percentage of depressed patients (60-80%), and are useful in alleviating vegetative and somatic depressive symptoms (e.g. decreased appetite/weight loss, early morning awakenings, psychomotor retardation etc..) by improving mood, increasing physical activity and alertness, and improving sleep and appetite. They appear to have less side effects than other antidepressants, although they take 2-4 weeks to work. They have also been shown to be effective for treating severe phobic, hypochondriacal and obsessive states, panic disorder and chronic pain. The heterocyclics, a newer class of antidepressant, are less toxic and work quicker than tricyclics. They work by slowing the reuptake of serotonin at the synapses. Their uses are similar to those of tricyclics, although they have less side effects than TCAs. Prozac is a type of heterocyclic has become the most widely-prescribed antidepressant, although it can produce serious side effects. The MAO inhibitors have been shown to be most effective for treating atypical kinds of depression that include symptoms such as anxiety and increased appetite, or depressions that have been resistant to other antidepressants. The most dangerous side effect is a hypertensive crisis, when taken with other drugs or specific foods.